Syndiotactic polystyrene (sPS) was first synthesized in 1985, using a homogeneous organometallic catalyst system based on a titanium compound and methylaluminoxane (MAO)(N. Ishihara, T. Seimiya, M. Kuramoto and M. Uoi, Macromolecules 1986, 19, 2465).
Syndiotactic polystyrene is a very attractive polymer. Its low specific gravity, low dielectric constant, high modulus of elasticity and excellent resistance to chemicals make syndiotactic polystyrene a promising material for a large number of applications in the automotive, electronic and packaging industries. However, sPS has poor impact strength.
Intensive researches to demonstrate the synthesis of sPS and the nature of other components, particularly catalysts and cocatalysts used in polymerization, have been conducted. However, problems in the polymerization process, such as reactor fouling and morphology control, have been revealed. Supported catalysts have been used to overcome said problems, but they have extremely low activity.
While the intensive researches on catalysts and polymerization process have been progressed, physical properties of syndiotactic polystyrene have been more focused. There are many patents about compounding and composite of syndiotactic polystyrene with other materials. Most of them disclose toughening of syndiotactic polystyrene by compounding with rubbery materials such as SEBS, SBS, SEP, SIS etc. The rest of them disclose compounding with other plastic materials such as polyolefin, nylon, polyesters etc. to balance physical properties of sPS or reduce cost However, there has not been a patent concerning syndiotactic polystyrene-based nanocomposite until now.
In general, phyllosilicates such as smectite clays, e.g., sodium montmorillonite and calcium montmorillonite are used for preparing polymer nanocomposites. Nonocomposites of nylon, PMMA, atactic polystyrene, polyester, etc. have been reported that they have substantially higher modulus and heat distortion temperature without significant increase of specific gravity as compared with corresponding neat polymers.
Several processes have been reported for preparation of a polymer nanocomposite. Melt mixing process is normally used for this propose, where planar silicate layers of clay are intercalated and exfoliated in the polymer matrix during the mixing process. Radical polymerization of a monomer in the presence of montmorillonite clay is another approach to obtain nanocomposite. However, polymerization via Ziegler-Natta or metallocene mechanism has difficulties because montmorillonite clay is hydrophobic.
Montmorillonite is hydrophobic which makes proper exfoliation and dispersion into conventional polymers difficult. Accordingly, special techniques are needed to disperse the layers of clay in nano-scale polymer matrix. The most common method is chemical treatment using organic compounds such as organic ammonium ion. The organic molecules are intercalated between adjacent planar silicate layers to increase the interlayer space between the adjacent silicate layers and to bond with a polymer.
Generally, the activity of a supported metallocene catalyst is about 1/100 times as low as that of a homogeneous catalyst. The preparation of a supported catalyst having an acceptable activity for syndiotactic polystyrene polymerization is more difficult because the polymerization activity of syndiotactic polystyrene is lower than that of polyolefine.
Direct loading of a metallocene catalyst on a montmorillonite clay is impossible because the support is hydrophobic.
Accordingly, the present invention discloses a new method for preparing a high activity metallocene supported catalyst system, particularly a supported catalyst for producing a syndiotactic polystyrene. Hydrophobic montmorillonite clay is used as a support and produces syndiotactic polystyrene having high activity.
The present invention provides a method for preparing new sPS nanocomposite and polyolefine nanocomposite by polymerization process using a nano-clay supported catalyst. The present invention provides sPS nanocomposite by the polymerization process and solves the problems of reactor fouling and morphology control when using a stirred-tank reactor.